The video conference system is the product of the combination of multimedia computer technology and communication technology. Integrated with multimedia and networking communication technology, the video conference system provides an environment to people at different locations to discuss problems and work in cooperation.
The system integrates the computer interaction, communication distribution and television authenticity, having evident superiority, thereby becoming a hot spot in computer field nowadays.
The early video conference system standard ITU-T H.320 is worked out by ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) in 1990. It is the fundamental standard for video conference system that based on electric circuit exchange bearing. With the development of TCP/IP technology, ITU-T came up with a new standard ITU-T H.323 in 1996. This new standard is video conferencing standard based on IP transmission network bearing, which is defined on general network architecture and has nothing to do with specific networks, therefore greatly extending its application range.
From the perspective of product, the H.323 video conference systems are varied and excelled with their own strong points, however, the products from different manufacturers are weak in interconnection and interworking, bringing inconvenience to the establishment of large-scale H.323 video conference system network. Within the current H.323 standardized video conference system, the MCU (Multi-point Control Unit) core-based media controller is responsible for transmitting audio and image data between each terminal. The number of terminals that the existing video conference system can hold is determined by the MCU capability, so in order to increase the users number, the MCU configuration must be improved. Therefore, the high investment including other hardware devices will inevitably influence the wide application of the video conferencing system.
The SIP standard is proposed by IETF (The Internet Engineering Task Force) organization in 1999. Its application goal is to realize real-time data, audio and video communication based on internet environment. Compared to H.323, the SIP (Session Initiation Protocol) is relatively easy and unrestrained, manufacturers can use existing network resources to deploy multimedia communication service, so it is able to construct a system satisfying the application needs with a low cost. Strictly speaking, SIP standard is a signaling standard that can realize real-time multimedia application. It adopts text-based encoding method and possesses large flexibility, expandability and cross-platform compatibility under point-to-point application environment. However, SIP protocol itself does not support multi-point conference function as well as management and control function, thus it is hard to meet the multi-point communication needs only by applying SIP system.
Therefore, a concept of “SIP video application server” is raised in the current SIP-based software video conference solutions. This application server is comprised of a Focus, a Media Policy server and a Conference Policies server. By using appropriate Media Policy and Conference Policies, the Focus can form the overall management control and media transmission solution of a conference, being responsible for conference management, media distribution and transmission. To a certain extent, the function of the Focus is similar to that of the MCU in the H.323 based video conference system. The system continues to use traditional C/S architecture and needs specialized media control server to control and process media. The capability of the server will determine the number of users that the system can support.